Nanoscale crystalline silicon powder

ABSTRACT

An aggregated crystalline silicon powder with a BET surface area of 20 to 150 m 2 /g is provided. The aggregated silicon powder may be doped with phosphorus, arsenic, antimony, bismuth, boron, aluminium, gallium, indium, thallium, europium, erbium, cerium, praseodymium, neodymium, samarium, gadolinium, terbium, dysprosium, holmium, thulium, lutetium, lithium, ytterbium, germanium, iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium, platinum, copper, silver, gold, or zinc.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of prior U.S. patentapplication Ser. No. 10/579,460, filed May 15, 2006, the disclosure ofwhich is incorporated herein by reference in its entirety. The parentapplication is the National Stage of PCT/EP04/12890, filed Nov. 13,2004, the disclosure of which is incorporated herein by reference in itsentirety. The parent application claims priority to German ApplicationNo. 10353995.6 filed Nov. 19, 2003, the disclosure of which isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention provides a nanoscale crystalline silicon powder and thepreparation and use thereof.

2. Description of the Related Art

It is known that an aggregated nanoscale silicon powder can be preparedin a hot wall reactor (Roth et al., Chem. Eng. Technol. 24 (2001), 3).The disadvantage of this process has proven to be that the desiredcrystalline silicon is produced along with amorphous silicon which isformed by the reaction of silane at the hot reactor walls. In addition,the crystalline silicon has a low BET surface area of less than 20 m²/gand thus is generally too coarse for electronic applications.

Furthermore, Roth et al. do not disclose a process in which dopedsilicon powders are obtained. Such doped silicon powders, with theirsemiconductor properties, are very important in the electronicsindustry. Furthermore, it is a disadvantage that silicon powder isdeposited on the reactor walls and acts as a thermal insulator. Thischanges the temperature profile in the reactor and thus also changes theproperties of the silicon powder.

DETAILED DESCRIPTION OF THE INVENTION

The object of the invention is the provision of a silicon powder whichavoids the disadvantages of the prior art. In particular, the siliconpowder should be one with a uniform modification.

The invention is also intended to provide a process by which this powdercan be prepared on an industrial scale in an economically viable manner.

The invention provides an aggregated crystalline silicon powder with aBET surface area of 20 to 150 m²/g.

In a preferred embodiment, the silicon powder according to the inventionmay have a BET surface area of 40 to 120 m²/g.

The expression aggregated is understood to mean that the spherical orlargely spherical particles which are initially formed in the reactioncoalesce to form aggregates during the course of further reaction. Theextent of growth may be affected by the process parameters. Theseaggregates may form agglomerates during the course of further reaction.In contrast to aggregates, which generally cannot or can only partly bebroken down into the primary particles, agglomerates form only a looseassociation of aggregates which can easily be broken down into theaggregates.

The expression crystalline is understood to mean that at least 90% ofthe powder is crystalline. This degree of crystallinity can bedetermined by comparing the intensities of the [111], [220] and [311]signals of the powder according to the invention with those of a siliconpowder of known crystallinity and crystallite size.

In the context of the invention, a silicon powder with a degree ofcrystallinity of at least 95%, particularly preferably one with at least98% crystallinity, is preferred. The evaluation of TEM images and thecounting of primary particles which exhibit lattice lines, as a featureof the crystalline state, is suitable for determining this degree ofcrystallisation.

Furthermore, the silicon powder according to the invention may be doped.The doping components may be phosphorus, arsenic, antimony, bismuth,boron, aluminum, gallium, indium, thallium, europium, erbium, cerium,praseodymium, neodymium, samarium, gadolinium, terbium, dysprosium,holmium, thulium, lutetium, lithium, ytterbium, germanium, iron,ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium,platinum, copper, silver, gold or zinc.

Particularly preferred, especially when used as a semiconductor inelectronic components, the doping components may be the elementsphosphorus, arsenic, antimony, bismuth, boron, aluminum, gallium,indium, thallium, europium, erbium, cerium, praseodymium, neodymium,samarium, gadolinium, terbium, dysprosium, holmium, thulium, ytterbium,lutetium. The proportion of these present in silicon powder according tothe invention may be up to 1 wt. %. In general, a silicon powder isrequired in which the doping component is present in the ppm or even theppb range. A range of 10¹³ to 10¹⁵ atoms of doping component per cm³ ispreferred.

Furthermore, it is possible for silicon powder according to theinvention to contain lithium as a doping component. The proportion oflithium present in the silicon powder may be up to 53 wt. %. Siliconpowder with up to 20 to 40 wt. % of lithium may be particularlypreferred.

Similarly, silicon powder according to the invention may containgermanium as a doping component. The proportion of germanium present inthe silicon powder may be up to 40 wt. %. Silicon powder with up to 10to 30 wt. % of germanium may be particularly preferred.

Finally, the elements iron, ruthenium, osmium, cobalt, rhodium, iridium,nickel, palladium, platinum, copper, silver, gold, zinc may also bedoping components in the silicon powder. The proportion of these presentmay be up to 5 wt. % of the silicon powder.

The doping components may be uniformly distributed in the powder or theymay be enriched or intercalated in the shell or the core of the primaryparticles. The doping components may preferably be incorporated atsilicon lattice sites. This depends substantially on the type of dopingmaterial and on reaction management.

A doping component in the context of the invention is understood to bethe element present in the powder according to the invention. A dopingmaterial is understood to be the compound used in the process in orderto obtain the doping component.

The silicon powder according to the invention may also have a hydrogenloading of up to 10 mol. %, wherein a range of 1 to 5 mol. % isparticularly preferred. NMR spectroscopic methods such as, for example,¹H-MAS-NMR spectroscopy or IR spectroscopy are suitable for determiningthis.

The invention also provides a process for preparing the silicon powderaccording to the invention, characterised in that

-   -   at least one vaporous or gaseous silane and optionally at least        one vaporous or gaseous doping material, an inert gas and    -   hydrogen    -   are subjected to heat in a hot wall reactor,    -   the reaction mixture is cooled down or allowed to cool down and    -   the reaction product is separated from the gaseous substances in        the form of a powder,    -   wherein the proportion of silane is between 0.1 and 90 wt. %,        with respect to the sum of silane, doping material, hydrogen and        inert gases, and    -   wherein the proportion of hydrogen, with respect to the sum of        hydrogen, silane, inert gas and optionally doping material is in        the range 1 mol. % to 96 mol. %.

Particularly advantageously, a wall-heated hot wall reactor may be used,wherein the hot wall reactor has a size such that as complete aspossible conversion of the feedstock and optionally of doping materialis achieved. In general the residence time in the hot wall reactor isbetween 0.1 s and 2 s. The maximum temperature in the hot wall reactoris preferably chosen in such a way that it does not exceed 1000° C.

Cooling the reaction mixture may be performed, for example, by externalwall-cooling of the reactor or by the introduction of an inert gas in aquenching process. A silane in the context of the invention may be asilicon-containing compound which provides silicon, hydrogen, nitrogenand/or halogens under the conditions of reaction. SiH₄, Si₂H₆, ClSiH₃,Cl₂SiH₂, Cl₃SiH and/or SiCl₄ may preferably used, wherein SiH₄ isparticularly preferred. In addition, it is also possible to useN(SiH₃)₃, HN(SiH₃)₂, H₂N(SiH₃), (H₃Si)₂NN(SiH₃)₂, (H₃Si)NHNH(SiH₃),H₂NN(SiH₃)₂.

Preferably, hydrogen-containing compounds of phosphorus, arsenic,antimony, bismuth, boron, aluminum, gallium, indium, thallium, europium,erbium, cerium, praseodymium, neodymium, samarium, gadolinium, terbium,dysprosium, holmium, thulium, ytterbium, lutetium, lithium, germanium,iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium,platinum, copper, silver, gold, zinc can be used. Diborane and phosphaneor substituted phosphanes such as tBuPH₂, tBu₃P, tBuPh₂P andtrismethylaminophosphane ((CH₃)₂N)₃P are particularly preferred. In thecase of lithium as a doping component, it has proven most beneficial touse the metal lithium or lithium amide LiNH₂ as the doping material.

Mainly nitrogen, helium, neon or argon may be used as an inert gas,wherein argon is particularly preferred.

The invention also provides use of the powder according to the inventionto produce electronic components, electronic circuits and electricallyactive fillers. The silicon powder according to the invention is free ofamorphous constituents and has a high BET surface area. The processaccording to the invention does not lead to the deposition of silicon onthe reactor wall, as is described in the prior art. Furthermore, theprocess according to the invention enables the production of dopedsilicon powder.

EXAMPLES

-   Analytical techniques: The BET surface area is determined in    accordance with DIN 66131. The degree of doping is determined using    glow discharge mass spectrometry (GDMS). The hydrogen loading is    determined using ¹H-MAS-NMR spectroscopy.    Apparatus used:-   A tube with a length of 200 cm and a diameter of 6 cm is used as a    hot wall reactor. It consists of quartz glass or Si/SiC with a    quartz glass liner. The tube is heated to 1000° C. externally using    resistance heating over a length of 100 cm.-   A SiH₄/argon mixture (mixture 1) of 1000 sccm of silane (standard    centimeter cube per minute; 1 sccm=1 cm³ of gas per minute with    reference to 0° C. and atmospheric pressure) and 3000 sccm of argon    and a mixture of argon and hydrogen (mixture 2), 5000 sccm of each,    are supplied from above the hot wall reactor via a two-fluid nozzle.    The pressure in the reactor is 1080 mbar. The powdered product is    separated from gaseous substances in a downstream filter unit.-   The powder obtained has a BET surface area of 20 m²/g.-   Examples 2 to 6 are performed in the same way as example 1, but the    parameters are modified. The parameters are given in table 1.

TABLE 1 Process parameters and physico-chemical values of the siliconpowders Example 1 2 3 4 5 6 Mixture 1 SiH₄ sccm 1000 250 500 1000 2502000 Argon sccm 3000 3750 3500 2800 3150 1000 B₂H₆ sccm — — — 200 — —(tBu)₃P sccm — — — — 600 — Mixture 2 Hydrogen sccm 5000 25000 10000 500025000 0 Argon sccm 5000 5000 5000 5000 5000 5000 BET Si powder (approx.)m²/g 20 140 50 20 140 7.5 H loading mol % 1.3 3.5 — n.d. n.d. n.d.Degree of doping ppm — — — 2400 480 —

1. A silicon powder consisting of aggregated spherical crystallinesilicon particles obtained by coalescence of spherical silicon particlesin the reaction zone of a hot wall reactor, wherein the aggregatedcrystalline silicon powder has a BET surface area of 20 to 150 m²/g. 2.The silicon powder according to claim 1, wherein the BET surface area isfrom 40 to 120 m²/g.
 3. The silicon powder according to claim 1,comprising at least one doping component selected from the groupconsisting of phosphorus, arsenic, antimony, bismuth, boron, aluminium,gallium, indium, thallium, europium, erbium, cerium, praseodymium,neodymium, samarium, gadolinium, terbium, dysprosium, holmium, thulium,lutetium, and ytterbium.
 4. The silicon powder according to claim 3,wherein a proportion of the at least one doping component is fromgreater than 0 up to 1 wt. %.
 5. The silicon powder according to claim1, further comprising hydrogen, wherein a hydrogen content is fromgreater than 0 to 10 mol. %.
 6. The silicon powder according to claim 2,further comprising hydrogen, wherein a hydrogen content is from greaterthan 0 to 10 mol. %.
 7. The silicon powder according to claim 3, furthercomprising hydrogen, wherein a hydrogen content is from greater than 0to 10 mol. %.
 8. The silicon powder according to claim 4, furthercomprising hydrogen, wherein a hydrogen content is from greater than 0to 10 mol. %.
 9. The silicon powder according to claim 1, which is freeof amorphous constituents.
 10. The silicon powder according to claim 2,which is free of amorphous constituents.
 11. The silicon powderaccording to claim 5, which is free of amorphous constituents.
 12. Thesilicon powder according to claim 6, which is free of amorphousconstituents.
 13. An electronic component, electronic circuit orelectrically active filler comprising the silicon powder according toclaim
 1. 14. An electronic component, electronic circuit or electricallyactive filler comprising the silicon powder according to claim
 2. 15. Anelectronic component, electronic circuit or electrically active fillercomprising the silicon powder according to claim
 5. 16. An electroniccomponent, electronic circuit or electrically active filler comprisingthe silicon powder according to claim 6.